Device and method for cooling and thermal conditioning of a tubular object

ABSTRACT

A device ( 1 ) for cooling and/or thermal conditioning of hot preforms or parisons ( 6 ), in particular of parisons for the production of blow-moulded bottles made of plastic material, limits and/or reduces the deformations of said parisons during cooling by containing the transverse deformations of the end close to the opening ( 8 ) of the parison. The device is provided with a tubular portion of prolongation which wraps totally around the parison that rests on its internal surface with one of its sections ( 9 ). Described herein is the corresponding method for cooling the parison ( 6 ).

FIELD OF THE INVENTION

[0001] The present invention relates to a device and a method forthermal conditioning of moulded objects, and in particular thermalconditioning of tubular objects such as parisons for the production ofplastic bottles by blow-moulding, reducing the deformations of theparisons upon their extraction from the injection mould.

PRIOR ART

[0002] In the production of blow-moulded bottles or containers made ofplastic materials, for example bottles or jars made of PET forfoodstuffs, beverages, mineral water, fruit juices, preserves, and thelike, one process of fabrication is that of injection-moulding of theparisons, from which may be obtained, in a subsequent operation ofstretch-blow-moulding, the finished container with even a considerablelapse of time between the production of the parison and the operation ofblowing; i.e., after the injection-moulding operation, the parisons arecooled and stored, or else taken to the blow-moulding, plant, which islocated in a different production site.

[0003] Cooling of the parisons can be obtained by extracting them fromthe injection mould when they are still hot and relatively plastic, butin any case of a consistency such that they may be gripped andtransferred into special containers with circulation of coolant, knownas cooling beakers or tubes or moulds, where the cooling operation iscompleted.

[0004] With the aim of increasing the rate of output ofinjection-moulding presses, one trend is that of extracting the parisonfrom the injection mould at the highest temperature possible, but thisincreases all the critical aspects of manipulation of the parison onaccount of its considerable plasticity and susceptibility to gettingdamaged during transfer to the cooling devices outside the press.

[0005] Another trend is that of cooling the parison as fast as possible,both to obtain a higher productivity, and so that the plastic materialof the parison will be as amorphous as possible.

[0006] In addition, according to some state-of-the-art productionsystems, the parison is extracted from the injection mould using variousdevices for mechanical gripping, for example mechanical grippers, andtransferred as fast as possible into the cooling beaker. If thetemperature of extraction is excessively high, and the parisonexcessively plasticized, the latter is deformed also by the mechanicalaccelerations and by the impact during handling. Consequently, a problemthat can arise during this second cooling step is that the parison, onaccount of thermal contraction or mechanical stresses, is deformed,assuming a bent shape, even with a few millimetres of misalignmentbetween the two ends of the parison.

[0007] This can lead to various types of problems; for example, numerousrejects during the subsequent operation of heating of the parison priorto the operation of blowing. The parison is pre-heated in an infraredfurnace, the lamps or heating surfaces of which pass very dose to theparison, and owing to the excessive deformations of the latter, bangagainst it, or else heat it in an uneven way, so bringing about furtherdeformations. In addition, the shape tolerances are a parameteraccording to which the quality and the reliability—and hence theprofit—of a possible external subsupplier of parisons, and in general ofany production process, whether internal or external, are measured. Afurther disadvantage that may occur is that a deformed parison, afterthe operation of stretching with as special bar gives rise, in thebottom, region of the stretched solid, to non-uniform wall thicknesses,which in the subsequent operation of blow-moulding of the bottle leadsto bursts.

[0008] One method according to a current technique for preventinggeometrical errors is that of inserting into the parison, which is inturn inserted into the cooling beaker, a force plug, plunger or mandrelfor preventing bends from occurring, which, however, leads to the needfor an additional plug-carrying plate and the movement of an additionalmechanical member in the cycle time of the machine.

[0009] Other solutions have been devised for prolonging the cooling ofthe parison in the injection mould without delaying too much the outputrate of the injection-moulding press.

[0010] A problem that the present invention seeks to solve is that ofreducing or eliminating the deformations that a parison may undergoduring cooling for thermal conditioning, or that it may have undergonebefore cooling for thermal conditioning after the injection-mouldingoperation is completed, with a high repeatability of the productionprocess.

[0011] Another purpose that the present invention seeks to achieve is tosimplify the state-of-the-art devices for eliminating the aforesaiddeformations, for example without recourse to the use of containmentplugs inside the parison in the cooling beaker.

[0012] The above purposes are achieved by a device having thecharacteristics according to Claim 1, and with a method having thecharacteristics according to Claim 16.

[0013] Advantages that are obtained by means of the present invention,in addition to the solution of the problems described above and to theimplementational simplicity of the invention, are the fact of enablingextraction of the parison from the injection mould at a highertemperature with limited deformations on the cooled parison. Inaddition, cooling beakers according to the present invention can bereplaced on already existing plants for cooling or thermal conditioningand blow-moulding, without having to make other modifications to theplant, at extremely contained costs and during a customary extraordinarymaintenance operation by staff that may even be not particularly highlyqualified. Some particular embodiments of the invention presented in thedependent claims regard, devices for extraction of the parison from thecooling device and/or thermal-conditioning device.

LIST OF FIGURES

[0014] Further advantages that may be achieved with the presentinvention will become apparent, to the person skilled in the sector,from the following detailed description of two non-limiting examples ofparticular embodiments, with reference to the attached figures, ofwhich:

[0015]FIG. 1 is a schematic side view of the internal body of a device,or cooling beaker, for cooling and/or thermal conditioning of a tubularobject, according to one first embodiment of the present invention;

[0016]FIG. 1A is a schematic sectional view according to the plane A-Aof the internal body of FIG. 1;

[0017]FIG. 1B is a schematic three-dimensional view of the internal bodyof FIG. 1;

[0018]FIG. 2 is a schematic sectional view of two assembled devices,according to the embodiment of FIG. 1;

[0019]FIG. 2A is a schematic side view of a first example of parison;

[0020]FIG. 2B is a schematic side view of a second example of parison;

[0021]FIG. 3 is a schematic three-dimensional view of mechanical meansfor extracting the parisons from a plurality of cooling beakersaccording to a particular embodiment of the present invention;

[0022]FIG. 3A is a detailed schematic view of the assembly made up ofmechanical means for extraction and cooling beakers represented in FIG.3;

[0023]FIG. 4 is a schematic side view of a second embodiment of a deviceaccording to the present invention;

[0024]FIG. 4A is a schematic sectional view according to the plane B-Bof the device of FIG. 4; and

[0025]FIG. 4B is a schematic three-dimensional view of the externalsleeve of the device of FIG. 4.

DETAILED DESCRIPTION

[0026]FIGS. 1, 1A, 2, and 2A are schematic representations of one detailand of the ensemble of a first preferred embodiment of a device for thetransport, cooling and/or thermal conditioning of tubular objects 6, inparticular, parisons, according to the present invention. In whatfollows, the said device is as a whole designated by the referencenumber 1, and alternatively also referred to as cooling beaker.

[0027] Cooling beakers of this sort, which in themselves are well knownto the current art, are used for example to complete cooling of theparisons, outside the injection mould with which they were produced, soas to be able to increase the output rate of the press. The parisons areextracted from the injection mould when they are still relatively hotand in a state in which they are more plastic and deformable than atroom temperature, but of a consistency such that they can be gripped,handled and moved. The beaker in FIGS. 2, 2A comprises an internal body2 on which is inserted externally a sleeve 3 made, like the body 2, of amaterial that is a good thermal conductor and preferably light, such asaluminium. In the external surface of the internal body 2 there are madehelical grooves 4 which, being closed by the sleeve 3, form channels fora coolant, for example water or some other appropriate fluid.

[0028] On its front side, the beaker 1 has an open front end 5 designedto enable introduction of a parison 6—or at least of its elongatedportion 10—which is to be cooled or thermally conditioned, into aninternal cavity 7 made in the internal body 2. The parison 6 of FIG. 2Acomprises a portion in the proximity of the open end 8 on which therecan be made, for example, the thread of the screw top of the futureblow-moulded bottle, an annular projection for tearing seals and forfixing tear tabs of the aforesaid bottle top, and a second annularprojection 9, also referred to in what follows as “ring”, whichtypically also has the purpose of making possible gripping and movementof the blow-moulded bottle in the processing stations set downstream orin the user's plants. Frequently, but not necessarily for the purposesof the present invention, the ring is also the maximum radial projectionof the region of the neck of the bottle (or anyway of the region closeto the open end 8). In general, the threaded region and that of the ringon the parison 6 already, have the same dimensions that they will haveon the blow-moulded bottle, whilst the elongated portion 10 and therounded and closed end 11 of the parison 6 are sized in such a way thatthey can be dilated by blow-moulding and, possibly, by biaxialstretching so as to assume the dimensions of the finished is bottle orcontainer. Since the present invention is particularly advantageous withparisons of elongated shape, in what follows the term “axial direction”or “longitudinal direction” shall mean the direction parallel to thelarger dimension of the parison, and by “radial direction”, “transversedirection” or “lateral direction” is meant the direction perpendicularto the larger dimension and to the axis of the parison or tubular object6. From the state of the art there is already known a wide range ofsystems for bestowing on the elongated portion 10, which is initiallyinserted very hot and easily deformable into the cooling beaker, a shapewith acceptable tolerances; for example, it is possible simply to leavea maximum play between the wall of the hot portion 10 to be expanded andthe wall of the internal cavity 7 of the internal body, for instance ofa few tenths of millimetre in the case of a parison that isapproximately 150 mm long. Obviously, this play will be reduced to zeroin the contact regions between the parison 6 and the walls of theinternal cavity 7; i.e., the gap between the parison and the walls ofthe internal cavity 7 varies locally from region to region of theparison 6. This fact limits the axial bending of the portion 10 that isto undergo expansion.

[0029] The modalities of contact or otherwise of the rounded end 11 ofthe parison with the bottom 12 of the internal cavity 7 of the internalbody, according to the known art, are numerous: for example, the end 11of the hot parison can be brought into contact with the bottom 12, orelse inserted at a distance and possibly brought into contact with thebottom 12, by deforming it in various ways or by sucking the entireparison towards the bottom 12.

[0030] According to certain solutions of the known art, the threaded endof the inserted parison 6 is allowed to project out of the beaker 1, inparticular when the parison 6 is introduced into the cooling beaker 1,bringing to bear upon it the ring 9 or other radial projection of theparison. In this case, particularly with parisons like the one in FIG.2A, with a part 13 close to the open end 8 having a tapered crosssection which is narrower than the remainder 14 of the bulb, if theparison 6 is not, for example, constrained by a plug inserted inside it,the open end 8,13, if cooled too fast, frequently bends considerably,since the narrower part 13 cannot be contained by the walls of theinternal cavity 7, and faulty parisons may be produced, with accentuatedelbow-like bends in the vicinity of the open end 8. The applicant hasencountered parisons of approximately 150 mm in length with errors oflinearity of even 2-3 mm or more between the ends of the parison.

[0031] Other deformations of the parison can result from the operationsof extraction from the injection mould and of transfer from this to thecooling beakers, all the more in that the current aim is to bringforward extraction and abbreviate the time for cooling the parison inthe mould. In certain cases the parison can thus prove excessivelyplastic, whilst the accelerations, decelerations and impact duringextraction, for example with mechanical grippers or the like, andmovement towards the cooling beakers 1, can also lead to deformationsthat are unacceptable for the customer or for the subsequent productionsteps.

[0032] According to the present invention, the cooling beaker or device1 is characterized in that it comprises containment means 15,represented in FIG. 1, designed to contain and/or reduce by contact theradial displacements of the open end 8 due to deformations of theparison 6, of thermal origin or deriving from the previous handlingoperations. In the preferred embodiment, represented in FIGS. 1, 1A, 2,the containing means 15 basically consist of a tubular portion withthrough lateral slits, so as to obtain a pair of prolongations on thefront part 5 of the internal body 2, preferably in a position which issymmetrical with respect to a meridian plane of the beaker 1, the saidslits extending in the longitudinal direction of the beaker. Withoutdeparting from the scope of the present invention, the frontprolongations which provide the containing means 15 can even be justone, which embraces the open end of the parison 6 with a sufficientangle of envelopment, or else they may number more than two. This isobtained by producing an appropriate number of through slits on the wallof the tubular portion.

[0033] The two prolongations 15 are shaped so as to define, on theinside of the beaker, supporting side surfaces 16, against which theopen end 8 of the parison 6 can rest laterally, i.e., in the radialdirection, following upon its deformation. In the example of FIG. 2A,each prolongation 15 defines a sector of substantially cylindricalsurface, against which the annular edge of the collar or ring 9 (i.e.,the part of the open end 8 of the parison that presents the maximumradial projection), or some other chosen region of the parison, comes torest, undergoing deformation on account of thermal shrinkage.

[0034] The shape of the internal cavity 7 and of the lateral supportingsurfaces 16, or else both of these, are defined, starting from thegeometry of the parison 6 in such a way as to adapt them to one another.

[0035] The supporting surface or surfaces 16 are shaped and sized insuch a way that, between the surface or surfaces and the section forsupporting the parison, chosen for contact, is set at least one minimumradial gap, or also a maximum radial interference, of a pre-set value.The said minimum radial gap, or maximum interference, can be calculatedwith reference to the dimensions of a parison 6 of nominal dimensionsand geometry or, equivalently, of a parison 6 at the temperature ofextraction from the injection mould, for example a few tenths ofmillimetres of radial gap between the edge of the ring and thecorresponding cylindrical surface of contact 16 made on theprolongations 15. In this case, advantageously a parison 6 can beinserted, by bringing its bottom 11 to bear upon the bottom 12 of thecavity 7, and, thanks to the cylindrical surface or surfaces 16, thering 9 will be contained laterally, but is free to slide longitudinallyowing to the thermal contraction caused by cooling.

[0036] Alternatively, the contact surface or surfaces 16 may be sectorsof a flared surface or may have the shape of a truncated cone whichopens towards the outside of the beaker 1, in order to allow also forthe thermal reduction of the diameter, for example, of the ring 9 orother region of contact on the open end 8.

[0037] The devices as defined above make i possible, once inserted intothe internal cavity 7, to straighten a parison 6 which is alreadydeformed by heat as a result of a previous automatic manipulation, forexample to transport it from the injection mould to the cooling beaker.

[0038] The surface above the cylindrical surface 16 (FIG. 2)advantageously—for example depending upon the ratio between the diameterof the elongated part of the parison and the external diameter of thering—may form an ample flaring that opens outwards so as to constitute alead-in for the parisons that are inserted into the cavity 7.

[0039] Advantageously, for example by aspirating the air inside theinternal cavity 7 through the channel 18 open on the bottom 12 of thecavity, there is produced a negative pressure for increasing the rate ofheat exchange between the parison 6 and the cooled internal body 2,notwithstanding the gap existing in some regions between the parison andthe walls of the internal cavity 7. Initially, when the material of theparison 6 is still considerably plastic, the negative pressure deformsalso the walls of the elongated portion 10, causing them to adhere tothe walls of the internal cavity 7.

[0040]FIGS. 3 and 3A are schematic representations of a further aspectof the preferred embodiment of FIG. 1. In accordance with the prior art,rows of a number of cooling beakers 1 are fixed on a plate or othersupport, which can be moved, for example, by a rotating arm. Thereference number 18 designates as a whole the mechanical means forextracting the parisons from the internal cavities 7 of the beakers.

[0041] The mechanical means 18 comprise a number of extraction bars 19that move in a longitudinal direction with respect to the beakers 1 andare actuated by a system of levers and hydraulic cylinders. Eachextraction bar 19 comprises a plurality of holes or cutaway regions 20,through which the cross section of one or more beakers 1 can pass.Present on the edges of the cutaway sections 20 are two teeth 21, orsome other similar type of radial projections, which are prolongedinside the beakers 1 through the longitudinal slits 22 that separate thetwo longitudinal prolongations 15 from one another and which, when thebars 19 are in the lowered position, are inserted under a region wherethere is a radial expansion of the cross section of the end 8 of aparison, for example under the ring 9. When a hydraulic cylinder isactuated, the corresponding extraction bar 19 is raised, translatingparallel to itself along the axis of the beakers 1. The pairs of teeth21 sliding in the slits 22 bear upon the rings 9, or other regions ofradial expansion of the sections 8 of the parsons, and extract a row ofparisons 6 from the corresponding beakers 1. The radial projections 21may also have different shapes, even ones not resembling teeth, providedthat they are capable of extracting the parisons 6 from the beakers 1.

[0042]FIGS. 4, 4A and 4B relate to a second preferred embodiment of thepresent invention, in which the tubular portion that forms a pair ofprolongations 15 is obtained as a prolongation of the external sleeve 3instead of the internal body 2. The criteria of sizing the internalcavity 7 of the internal body 2, and the determination of the gaps andof the play between the portion 10 of the parison that is to undergoexpansion and the open end 8, and between the walls of the cavity 7 andthe supporting surfaces 16 are similar to the preferred embodimentdescribed previously. This second embodiment is simpler to produce, andcan be mounted on a pre-existing internal body not provided withprolongations 15. In addition, a “change of format” can be obtained in asimpler way, in the sense that, by changing the external sleeve 3, aninternal body 2 can house, for example, both a parison 6 for bottleswith standardized rings having an external diameter of 28 mm, of thetype illustrated in FIG. 2A, and a parison with a ring having astandardized external diameter of 38 mm, of the type illustrated in FIG.2B.

[0043] Without departing from the scope of the present invention, thedevices described above may undergo numerous modifications. For example,in addition to undergoing modifications that are within the reach of aperson skilled in the sector, the said devices can find application inthe thermal conditioning of parisons for containers or moulded objectsmade of materials other than polyethylene terephthalate, such as HDPE,PP, and PE.

1. A device (1) for cooling and/or thermal conditioning of a hot tubularobject (6) provided with a first closed end and a second open end (8),in which the device (1) comprises a tubular internal cavity (7) providedwith an open end (5) for the introduction of said tubular object (6) andshaped in such a way as to accommodate a first portion (10) of saidtubular object (6) set in the proximity of said first closed end and tocontrol the deformations thereof, the said device being characterized inthat containment means (15) are provided, designed to contain and/orcontrol, by means of contact on the outside of a second portion of saidtubular object (6) in the vicinity of said second open end (8), thedeformations that are produced, in a direction transverse to the axis,during cooling and/or thermal conditioning; of said tubular object (6).2. The device according to claim 1, in which the containment meanscomprise a tubular element (15), coaxial to said tubular internal cavity(7) of which it constitutes a prolongation, and the internal surface(16) of which constitutes a support for the second portion of saidtubular object (6).
 3. The device according to claim 2, in which thetubular element (15) is provided with at least one through longitudinalslit (22) that forms a discontinuity in the internal supporting surface(16).
 4. The device according to claim 3, in which said internalsupporting surface (16) has a dimension such that, at the temperature ofinsertion of the hot tubular object (6) into the internal cavity (7),there is set at least one minimum radial gap or a pre-set maximum radialinterference.
 5. The device according to claim 4, in which the internalsupporting surface (16) is shaped in such a way that it can rest againsta section (9) of the second portion of said tubular object (6)comprising the maximum radial projections.
 6. The device according toclaim 1, in which the internal cavity (7) contains and constrains, atleast partially, thermal deformations of the first portion (10) of thetubular object (6), and is of diameter such as to produce, with the wallof the tubular object, a gap of a size not greater than a pre-setmaximum amount after cooling.
 7. The device according to claim 3, inwhich it comprises an internal body (2) and a coaxial external sleeve(3) fitted on the internal body (2).
 8. The device according to claim 7,in which said tubular element (15) constitutes an axial prolongation ofthe internal body (2).
 9. The device according to claim 7, in which saidtubular element (15) constitutes an axial prolongation of the externalsleeve (3).
 10. The device according to claim 3, in which the internalsupporting surface (16) is substantially cylindrical.
 11. The deviceaccording to claim 3, in which the internal supporting surface (16)substantially has the shape of a truncated cone, and widens towards theopen end of the device.
 12. The device according to claim 3, in whichmechanical means (18) are provided for extraction of the tubular object(6) from the internal cavity (7).
 13. The device according to claim 12,in which the mechanical means of extraction comprise a plate providedwith a hole of diameter greater than the diameter of the tubular element(15) and provided with at least one radial tooth (21) designed to slidealong said longitudinal slit (22) for pushing the tubular object (6) inthe longitudinal direction.
 14. A cooling tower for tubular objects (6)characterized in that it comprises a plurality of cooling devices (1) inaccordance with any one of claims from 1 to
 13. 15. The cooling toweraccording to claim 14, in which the mechanical means (18) of extractioncomprise one or more extraction bars (19) for extracting simultaneouslya plurality of tubular objects (6) from a corresponding plurality ofsaid cooling devices (1).
 16. A method for cooling at least one hottubular plastic object (6), implemented by means of a cooling device (1)according to claim 1, comprising the following steps: a) injectionmoulding of the tubular object (6) in an injection-moulding press; b)extraction of said tubular object (6) at a first temperature at whichthe structure is still very plastic and deformable; c) insertion of saidtubular object (6) throughout its length in the internal cavity (7) ofthe cooling device (2); and d) withholding, during a pre-set period, ofsaid tubular object (6) inside said cooling device (2) until a secondlower temperature than said first temperature is reached.
 17. Thecooling method according to claim 16, which envisages the stage ofextraction of the tubular object from the cooling device by mechanicalmeans (18).